CVE-2023-54039

What it actually does

Out-of-bounds memory read in j1939_tp_tx_dat_new() caused by memcpy using skb->cb size instead of struct j1939_sk_buff_cb size, allowing access beyond the intended structure bounds in the Linux kernel CAN J1939 stack.

Why it matters to the business

Systems relying on J1939 CAN protocol in embedded Linux environments face risk of kernel instability or memory exposure; the low exploit maturity and absence from known campaigns limit immediate operational disruption but still require patching in affected distributions.

How an attack unfolds

An attacker with local access or ability to influence J1939 socket operations triggers j1939_tp_tx_dat_new(), causing the oversized memcpy to read past the j1939_sk_buff_cb structure and potentially leak kernel memory or cause a crash.

How to fix it

Update the Linux kernel to a version containing commit d2136f05690c272dfc9f9d6efcc51d5f53494b33 or later; rebuild and deploy images such as terraform-fips-1.12 1.12.2-r0 or equivalent that incorporate the corrected j1939 code and BUILD_BUG_ON check.

How to confirm the fix worked

Confirm kernel source contains the updated memcpy using sizeof(struct j1939_sk_buff_cb) and the BUILD_BUG_ON assertion; verify running kernel version matches or exceeds the fixed commit and test J1939 socket operations for absence of out-of-bounds faults.

Typical attack path

1. Gain local execution or network adjacency to a J1939-enabled Linux system
2. Create or manipulate a J1939 socket buffer with cb size exceeding struct j1939_sk_buff_cb
3. Invoke transport data transmission path that reaches the vulnerable memcpy
4. Observe resulting memory read or kernel fault for information disclosure or denial of service

How to detect it

Review kernel logs for J1939-related faults or oops messages around socket buffer handling; examine system call traces involving j1939_tp_tx_dat_new and check for unexpected memory access violations in CAN subsystems.

What your security team should do

• Prioritize kernel updates on any systems exposing J1939 interfaces
• Audit embedded or automotive Linux deployments for use of the affected protocol stack
• Monitor for new exploit maturity indicators given the memory corruption nature
• Apply the patch across all derivative distributions before the next major release cycle